This invention relates to the art of blow molding from a parison of articles of organic plastic material susceptible to the improvement of their properties by orientation and has for its principal objects the provision of an apparatus which is characterized by a more rapid operating cycle with less effect upon the temperature of the parison, carrying out the steps of parison production, stretch orientation and circumferential orientation in a single uninterrupted, yet completely controlled sequence, and the provision of improved, oriented hollow articles.
The art teaches various methods and apparatus for obtaining blow molded articles of organic plastic material from a parison, such as in U.S. Pat. No. 3,349,155 and U.S. Pat. No. Re. 27,104. Generally, these methods are characterized by forming a parison in a parison mold on a blow core, placing said formed parison and blow core into a blow mold and expanding said parison in the blow mold by means of fluid pressure.
While the blow molding operation tends to impart orientation to the article, such orientation is predominantly circumferential, i.e., not bi-axial. Also, the degree of such orientation is difficult to control. It is therefore difficult to obtain the advantageous properties in the article that bi-axial orientation is capable of providing.
It is known that the control of orientation depends largely upon the control of the temperature of the parison just prior to orientation. It is found that such temperature control is best obtained by enclosing the article prior to the orienting step in an environment, usually a tempering mold, that imparts temperatures to the regions of the parison corresponding to the degree of deformation that is intended for such regions.
It is naturally commercially desirable to process a plurality of parisons at the same time. However, hollow articles to be made from parisons are usually much larger than the parisons themselves and hence cannot be accommodated in their respective molds with the same center spacing as the parisons. Therefore, problems arise when a plurality of parisons are made in parison molds and thereafter also tempered in a plurality of tempering molds having a different center spacing than the plurality of blow molds into which the parisons are to be transferred.
It is, therefore, a principal objective of the present invention to provide an apparatus and method which accommodates the differential center spacing of the parisons and the final blown object.
It is an additional object of the present invention to provide such an apparatus and method which conveniently, expeditiously and inexpensively accommodates the differential center spacing of the parisons and the blown object without interfering with a rapid operating cycle.
Further objects and advantages of the present invention will appear hereinbelow.